Batteries as principal or backup power sources have numerous applications in such industries as computer technology and telecommunications. In these applications, it is important that the battery be maintained at a fully charged condition in order to function properly when needed.
One particular application for batteries is as an emergency power source for telecommunications equipment located outdoors. If the regular power supplied by an AC source fails, the battery must be able to provide the necessary voltage until such time as the AC power is restored. It is common in such applications that a battery charger be connected across the batteries such that they are constantly maintained at the proper voltage levels. In a 48 volt DC battery string, the charge currents from the AC rectifier can be large enough that the voltage drop across the charging leads is noticeable. Since small changes in voltage at the batteries are significant in controlling the rate of charge, it has been found that minor errors in charge control are introduced when the battery voltage is measured across the battery terminals using long sense leads connected to the voltage measurement circuit.
In U.S. Pat. No. 5,666,040 granted to Bourbeau, a networked battery monitor control system and charging method is disclosed in which individual battery conditions are detected for each battery in a string of batteries by electronic modules. The electronic modules produce a go/no-go signal for each of four battery conditions: over-voltage, under-voltage, over-temperature and float-voltage. The go/no-go signals are read by a network controller connected to each module via a single three-wire local area network (LAN). Over-voltage to any individual battery can be limited by connecting by-pass resistors across individual batteries. Charging current to the string of batteries can be adjusted by the controller in response to over-voltage detected by one or more of the modules connected to the individual batteries in the string. In Bourbeau, the battery charger current and voltage are not variably controlled in response to a variable battery voltage. The object of the Bourbeau reference is to provide a simplified networked battery monitor and control system in which the individual characteristics of each battery in a string of batteries can be monitored and compensated while allowing the battery string to be charged and discharged as a group.